The importance of achieving accurate mutual alignment of individual components in any optical system is well known. The miniature dimensions of components used in modern optical communication systems render such alignment difficult both to achieve and to maintain. For example, one problem in the construction of laser transmitters is that of efficiently coupling the optical output from a laser diode into an optical fiber. To obtain efficient coupling, the fiber end is desirably precisely aligned with the emitting area of the laser. When such alignment is achieved, the fiber is then fixed in place, ideally by a method that ensures alignment is sustained throughout the device lifetime.
The current methods of obtaining an initial alignment between an optical fiber and a laser output port are primarily a raster scan or a spiral scan. An exemplary embodiment of a raster scan is shown in FIG. 1A, and an exemplary embodiment of a spiral scan is shown in FIG. 1B. The scans are characterized by their data points 1–16 and 100–119, respectively, whereby the scan obtains a measure of alignment quality (i.e., coupled optical power) at each data point in the sequence indicated by the arrows. The optical fiber is initially fixed to an X-Y linear movement table and positioned in front of a stationary laser diode output port. The laser diode is activated, and the scan proceeds to activate the linear table, moving the optical fiber along the respective paths indicated in FIGS. 1A–B for raster and spiral scans. At each of the predefined positions 1–16 and 100–119, data is collected about the alignment quality between the optical fiber and the laser output face. A determination is then made as to the location of the predefined position with the highest, or otherwise desirable, alignment quality. A position of final alignment may then be designated at the predefined position with the desired alignment quality.
Such scans are useful for characterizing the input and output ports (i.e., optical fiber face and laser output face), but are generally time consuming in a manufacturing process. For example, a raster scan may be characterized by a 6 micron square with 0.3 micron resolution for an initial low resolution scan, and a 1 micron square with 0.09 micron resolution for a final high resolution scan. Such a scan may require the gathering of 521 data points, whereby each data point may require 100 milliseconds to be processed. In a typical raster scan described above, therefore, approximately 52 seconds may be needed for the complete scan.
It can be seen, therefore, that the large number of data points used in the alignment process typically take an undesirable amount of time to collect and analyze. Furthermore, the final coupling efficiency that is achieved may not always be the highest coupling efficiency that is possible for a particular interface due to an undesirably large number of data points needed for a high resolution scan.